This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Complexes comprising siRNA and lipidic aminoglycoside derivatives have been recently imaged by Cryo-EM, displaying a typical layered microstructure. In our lab we prepared lipid-siRNA constructs using a variety of lipid systems which have been successfully employed in gene silencing activities. The lipid-siRNA phase behavior appears to be very rich and so far we have identified by X-ray scattering three categories of supramolecular structures. Specifically: i) a lamellar phase obtained with commercially available cationic/non-ionic lipids, ii) a 2D hexagonal structure obtained with multivalent cationic lipids synthesized in our lab, and finally iii) a bicontinuous cubic phase obtained by a combination of a "cubic forming" neutral lipid and "home synthesized" multivalent cationic lipids (as well as commercially available). In addition, we have observed that the nature of the phase has a great impact on SE. We propose Cryo-EM experiments to obtain 2D images of the lipid nanoparticles alone and upon aggregation with siRNA. Our long-term goals are to locate the siRNA domains in the lipid-siRNA aggregate.